The present invention relates to a method and apparatus for controlling the operation of a short circuit testing system, particularly a system for sequentially testing the insulation of a plurality of conductors to ground.
In the manufacture and maintenance of high voltage electrical equipment, such as generators and motors, it is necessary to test the insulation between individual conductors and ground. This can be done, for example, by measuring the resistance between each conductor and ground, utilizing a megohmeter while a high voltage is applied between the conductor and ground. In order for such test to be reliable, it is necessary to assure that the proper connection has been established between the meter and both the conductor and a point at ground potential.
In addition, when a high voltage is applied to an insulated conductor, which will normally have a capacitive coupling to ground, the resulting charge accumulation will cause a voltage to remain between the conductor and ground for at least a certain period of time after the high voltage source has been disconnected. This remaining voltage can represent a shock hazard to operating personnel and could cause damage to the apparatus being tested.
In addition, each conductor being tested is normally connected to the meter via a relay, and it is desirable to confirm the proper functioning of the relay before application of the high voltage to the associated conductor.